In fact zero-based has shown some undeniable advantages over one-based. I couldn't explain it better than Dijkstra's famous essay:
http://www.cs.utexas.edu/~EWD/ewd08xx/EWD831.PDF
There are only a few languages that are purely for beginners (LOGO and BASIC?) so it's a high cost to annoy experienced programmers for something that probably isn't a big deal anyway.
Thus, 1 probably wasn't "easier", it just adhered to an existing orthodoxy that "beginners" came from at the time.